1. Technical Field
This disclosure relates to a wafer container with cushion sheets in which semiconductor wafers are set, carried and stored
2. Description of the Related Art
Thin semiconductor wafers are commonly stored in a wafer container so as prevent them from being broken, damaged and polluted when they are carried and stored during semiconductor manufacturing processes. Several containers have been proposed for use as such a wafer container. For example, one type of wafer container includes plural stacked wafer-mounting trays, and each semiconductor wafer is individually stored in an interior space formed between two wafer-mounting trays so that each wafer can be independently and safely stored. Hereinafter, “a wafer-mounting tray” means “a tray that mounts a wafer or wafers.” (For example, see JP2003-168731.)
Another type of wafer container includes cushion sheets in which one wafer is sandwiched between two cushion sheets in the interior space formed between two stacked wafer-mounting trays in order to safely store a semiconductor wafer that has become brittle by recent ultrathinning, such as an ultrathin semiconductor wafer that is 200 micrometers or less in thickness. In such a case, since the semiconductor wafer is sandwiched between two cushion sheets, it is protected from being broken and damaged by external forces such as vibration or impact. (For example, see JP2005-191419.)
Although the semiconductor wafer is kept flat when it is sandwiched between the two cushion sheets of two stacked wafer-mounting trays, the semiconductor wafer become warped by the existence of internal stress when the wafer-mounting trays are separated and the semiconductor wafer is no longer sandwiched between the cushion sheets. If such a variation in the sandwiched and not-sandwiched states is repeated many times, the semiconductor wafer may be broken and damaged. Further, even though the semiconductor wafer is theoretically always kept flat by being adhered on the cushion sheet, an ultrathin semiconductor wafer may be broken and damaged by the strong adhesive force when the wafer is separated from the cushion sheet.